1. Field of the Invention
The present invention relates to an electrophotographic organic photoreceptor, and more particularly, to a double-layered positively-charged organic photoreceptor.
2. Description of the Related Art
Double-layered positively-charged electrophotographic organic photoreceptors basically include a charge transport layer formed on an electroconductive support and a charge generating layer formed on the charge transport layer. An overcoat layer may be optionally formed on the charge generating layer, which has a small thickness, to protect it from wearing by attrition with toner or a cleaning blade. In addition, an adhesive layer for enhancing the adhesion between the electroconductive support and the charge transport layer or a charge blocking layer for blocking charge migration between the two layers may be formed.
An electrophotographic imaging process using such a double-layered positively-charged organic photoreceptor is described as follows. After positively charging the surface of an organic photoreceptor, a laser beam irradiates a charge generating layer to generate positive and negative charges. The positive charges are injected into a charge transport layer by an electric field applied to the organic photoreceptor and migrate to an electroconductive support. The negative charges migrate to the surface of the charge generating layer or an overcoat layer to neutralize surface charges. A surface potential varies by exposure, so that a latent image is formed in an exposed region. Then, this latent image is developed with toner and transferred to a receptor medium, such as paper.
Compared with single-layered organic photoreceptors requiring complex electrical properties for a single layer, double-layered positively-charged organic photoreceptors including two layers responsible for different functions may more easily control electrical properties, such as charge potential and exposure potential. Since a stable electric field may be applied to the thin layers, the charge generating layer and the charge transport layer, of a double-layered positively-charged organic photoreceptor, the photoreceptor may retain a larger amount of charge at a given field strength and develop images with a larger amount of toner. The double-layered positively-charged organic photoreceptor is compatible with wet toner as well as dry toner.
However, when a charge generating layer forming composition is applied to a charge transport layer in the manufacture of a double-layered positively-charged organic photoreceptor, the charge transport layer dissolves in an organic solvent contained in the charge generating layer forming composition, so that materials flow out of the charge transport layer and the charge transport layer becomes uneven. The uneven charge transport layer leads to a lower, fluctuating charge potential or to ineffective charge retention of the organic photoreceptor. In addition, the materials that flow out of the charge transport layer contaminate the charge generating layer forming composition.
To resolve these problems, using an organic solvent incapable of dissolving the materials composing a charge transport layer for a charge generating layer forming composition has been suggested.
However, in a double-layered positively-charged organic photoreceptor manufactured using the suggested method, the solid interface between the charge transport layer and the charge generating layer hinders charges generated in the charge generating layer by laser irradiation to enter the charge transport layer. As a result, a surface potential in the irradiated portion cannot drop sufficiently, and an exposure potential increases with repeated electrophotographic processes.